A confounding factor in selection for postponed aging may be the influence of deleterious genes which rise to high frequency due to genetic drift. Such deleterious genes could obscure the effects of beneficial genes favored by natural selection. The rate and magnitude of such inbreeding depression will depend on the effective population size. Allele frequency variation may also overwhelm the changes in allele frequencies produced by natural selection if the population is particularly small or selection particularly weak, making the effective population size a critical parameter. This proposal will estimate effective population size by direct measurement of male and female reproductive success in environments that are similar to those that the populations are maintained in. This research will provide one of the few detailed studies of the variability of male or female reproductive success in laboratory populations. For gene frequencies which can be assayed directly, the study of replicated laboratory populations can reveal changes in allele frequencies which are associated with particular selection regimes. Such changes may reveal selection directly on that gene or may reflect selection on a linked locus which has, due to linkage disequilibrium, affected the frequency of alleles at the linked neutral locus. In the populations selected for postponed aging, there has been a dramatic increase in a rare allele at the SOD locus, relative to the controls. To study such linked loci, this project would measure levels of linkage disequilibrium between the SOD gene and DNA markers at various positions within 10 kb of the SOD locus. Comparisons of linkage disequilibrium in the replicate populations will aid in distinguishing linkage arising from chance events peculiar to a single population from events, like selection, which should be common to all populations. In addition, the levels of linkage disequilibrium in the laboratory populations would be contrasted to that of a natural population as a means of identifying the consequences of prolonged laboratory maintenance on the genetic structure of Drosophila populations.